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arXiv · 1310.3065

Revisiting the crystal electric field of P2-NaxCoO2 for the intermediate spin state of Co3+

G. J. Shu·F. C. Chou
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Abstract

The magnetic moment per Co4+ of P2(gamma)-type NaxCoO2 in Curie-Weiss metal regime is revisited and examined under a newly proposed modification of the octahedral crystal electric field (CEF). The proposed model explains the origin of the existence of the intermediate state S=1 for Co3+ through an exciton-like elementary excitation of the narrow gap between the split eg and t2g groups. The CoO2 layer is proposed to be constructed from the tilted edge-sharing square-planar CoO2 chains with inter-chain coupling. The square-planar CEF of CoO2 requires covalent bond formation between Co and the four in-plane neighboring oxygens, while the oxygens sitting in the neighboring chains can be viewed as apical oxygens of low effective charge for a CoO6 pseudo-octahedron. The reason why angle-resolved photoemission spectroscopy (ARPES) failed to observe the local-density approximation (LDA) predicted e'g hole pockets at kz=0 and the reversed order of the t2g splittings between LDA and CEF calculations can also be resolved using the proposed model.

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G. J. Shu, F. C. Chou. 2013-10-11. Revisiting the crystal electric field of P2-NaxCoO2 for the intermediate spin state of Co3+. https://doi.org/10.1103/physrevb.88.155130

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